1. Field of the Invention
The present invention relates to a device for the leaktight attachment of semi-permeable membranes to the support plates of a separatory apparatus which separates by selective permeability.
2. Description of the Prior Art
Separatory apparatuses comprised of a plurality of planar, semi-permeable membranes and which separate fluid by selective permeability are known to this art; compare U.S. Pat. No. 3,831,763. These apparatuses comprise sub-units which are formed, in particular, by the juxtaposition of a number of membrane support plates, with the pressurized fluid to be treated, which is generally liquid, circulating in parallel between the membranes of the successive support plates (of one sub-unit), which are provided with generally elongated orifices towards each of their ends for the passage of the fluid. This fluid circulates in series from one sub-unit to the other due to the presence of so-called intermediate plates which only have an orifice towards one of their ends. The fluid which has passed through the membranes is recovered individually for each support plate, on the edge of the latter, by virtue of at least one tube provided for this purpose.
U.S. Pat. No. 3,809,246 has a proposed a solution to the problem of keeping the membranes leaktight near the orifices, for the passage of the fluid to be treated, of each support plate. This solution consists of keeping the transverse ends of the membrane in an elongated opening close to the orifice for the passage of the fluid to be treated by means of a detachable device which keeps the membrane leaktight on the inner wall of this opening. It has been shown that this detachable device can, under certain conditions of use of the apparatus, and in particular for high rates of circulation of the fluid to be treated, advantageously be replaced by a device, which is preferably of circular shape, at the center of which circulates the fluid to be treated.
A device of circular shape for the leaktight attachment of membranes to a support plate is already known, but it exhibits the disadvantage that it is not itself fixed to the support plate, which requires that the adjacent devices of two consecutive support plates be held in contact with one another, for example, by virtue of cams or peripheral ridges, in which case the membranes are only kept leaktight on the support plates when the apparatus is tightened up, e.g., clamped. This embodiment of the membrane-fixing device, therefore, only makes it possible to ensure the leaktight attachment of the membranes to each opposite face of a support plate and around the orifice provided for the passage of the fluid to be treated when the apparatus itself is tightened-up. This embodiment of the attaching devices, therefore, exhibits the disadvantage that it renders the leaktightness of the membranes on each support plate dependent on the tightening of the apparatus itself, which tightening must also make it possible to ensure the peripheral leaktightness between two consecutive membrane support plates.
A device which does not exhibit the disadvantages of the aforediscussed device is described in U.S. Pat. No. 4,165,082. This device comprises two rings which are fixed to one another, after they have been arranged in the orifice of the support plate, by bringing them together axially until the edge of each of them presses the membrane in a leaktight manner against each face of the said support plate. These rings are generally made of a rigid macromolecular material and are advantageously of an injection-molded substance. It would, however, be advantageous to make a suitable device from a material possessing superior temperature stability and resistance to chemical agents.